Owner's Manual

Bi-Amping is Often Superior to Bridged Mode

Bridging offers a massive power increase but It is often more power than your speakers need or can

safely handle. Bi-amping is an alternative to bridging and many people report greater sonic

improvements. Like bridging, bi-amping will require a A 21+ amplifier for each speaker.

Note: Bi-amping in this context is technically “passive bi-amping” so an external electronic crossover is

not required. The speaker LF and HF terminals still connect to the speaker’s passive crossover

circuits, the difference being that with passive bi-amping the LF and HF crossovers are powered

separately.

Connecting speaker wires for Bi-amping

Bi-amping requires speakers with separate LF (Low Frequency) and HF (High Frequency) input

terminals with removable metal straps or wires. (Some KEF speakers use a rotary switch to join or

separate the HF and LF sections). The left channel of the first A 21+ will power the LF section of one

speaker and this same A 21+’s right channel will power the HF section of the same speaker. The

second A 21+ will connect the same way to the right channel speaker’s LF and HF inputs. When bi-

amping both A 21+’s Bridged switches must be set to their Normal (Stereo) position.

Setting up the input wires for Bi-amping

The A 21+ has an RCA Loop Output jack for each channel. These looping outputs allow the input

signal from one channel to be daisy-chained to the other channel’s RCA Input jack. When bi-amping

you will connect a standard RCA cable from the loop output of the Left channel to the Input RCA jack

of the right channel. If you wish to connect your preamp with balanced XLR connections you will need

to purchase a pair of XLR “Y” cables. You cannot use a combination of a balanced XLR input and

RCA Loop Out to the other channel’s input because the balanced connections will play 6dB louder

than the RCA connections.

Note: Both amplifiers left and right channel gain controls should be set at the same position.

Speaker Connections

Speaker Terminals

The A 21+ speaker terminals accept speaker wires terminated with banana plugs, spade

connectors or up to 8 AWG bare wire.

Bare Speaker Wire Ends

If you plan to connect your speaker cables with bare wire ends, use a wire stripper to remove just enough

insulation to expose a 12" (13 mm) length of bare wire. You can insert the stripped wire into the hole that goes

vertically through each terminal’s metal post. Before inserting the wire, twist its bare strands tightly to prevent

any of the individual strands from making contact across the red plus and black minus speaker terminals. If

you have a soldering iron, you can “tin” (apply a small amount of molten solder) to each stripped bare wire to

prevent it from unraveling, fraying and oxidizing.

Correct Speaker Polarity is Important

Polarity refers to + and – connections. Speaker wires are coded with color, printing or a ridge on the insulation

on one of the leads so you know which lead was connected to the + and – terminals at the other end. This

coding will help you keep the + and - polarity consistent for all channels. If one speaker is wired with incorrect

polarity it will significantly impair sound quality.

Speaker Wire Length and Gauge (thickness)

When selecting speaker wire, follow these guidelines:

• Keep the length of your speaker wire as short as possible.

• Use the thickest wire practical. For lengths greater than 50 feet, use speaker wire with an

AWG (gauge) of 14 or lower. The smaller the AWG number, the thicker the wire.